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GENERIC HOT-PLUG APPLICATIONS

Power

Supply

0.1

µF

1000

µF

Optimum

2.7 V to 5.5 V

PC Board

Overcurrent Response

TPS2046B

OC1

GND

EN1

IN

EN2

OUT1

OUT2

OC2

Block of

Circuitry

Block of

Circuitry

DETAILED DESCRIPTION

POWER SWITCH

CHARGE PUMP

DRIVER

ENABLE (ENx)

TPS2045B, TPS2055B

TPS2046B, TPS2047B

SLVS532C – JULY 2004 – REVISED OCTOBER 2007

In many applications it may be necessary to remove modules or pc boards while the main unit is still operating.

These are considered hot-plug applications. Such implementations require the control of current surges seen by

the main power supply and the card being inserted. The most effective way to control these surges is to limit and

slowly ramp the current and voltage being applied to the card, similar to the way in which a power supply

normally turns on. Due to the controlled rise times and fall times of the TPS204xB/TPS2055B, these devices can

be used to provide a softer start-up to devices being hot-plugged into a powered system. The UVLO feature of

the TPS204xB/TPS2055B also ensures that the switch is off after the card has been removed, and that the

switch is off during the next insertion. The UVLO feature insures a soft start with a controlled rise time for every

insertion of the card or module.

Figure 28. Typical Hot-Plug Implementation (Example, TPS2046B)

By placing the TPS204xB/TPS2055B between the VCC input and the rest of the circuitry, the input power reaches

these devices first after insertion. The typical rise time of the switch is approximately 1 ms, providing a slow

voltage ramp at the output of the device. This implementation controls system surge currents and provides a

hot-plugging mechanism for any device.

The power switch is an N-channel MOSFET with a low on-state resistance. Configured as a high-side switch, the

power switch prevents current flow from OUT to IN and IN to OUT when disabled. The power switch supplies a

minimum current of 250 mA.

An internal charge pump supplies power to the driver circuit and provides the necessary voltage to pull the gate

of the MOSFET above the source. The charge pump operates from input voltages as low as 2.7 V and requires

little supply current.

The driver controls the gate voltage of the power switch. To limit large current surges and reduce the associated

electromagnetic interference (EMI) produced, the driver incorporates circuitry that controls the rise times and fall

times of the output voltage.

The logic enable pin disables the power switch and the bias for the charge pump, driver, and other circuitry to

reduce the supply current. The supply current is reduced to less than 1

μA or 2 μA when a logic high is present

on EN. A logic zero input on EN restores bias to the drive and control circuits and turns the switch on. The

enable input is compatible with both TTL and CMOS logic levels.

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Product Folder Link(s): TPS2045B TPS2055B TPS2046B TPS2047B